Selection of appropriate probiotic yeasts for use in dairy products: a narrative review

Abstract

Yeasts, with a history of approximately 5,000 years in food and medicinal applications, play a vital role in various industries. The advantages of these microorganisms include probiotic effects, phytate biodegradation, mycotoxin breakdown, and adsorption capabilities. Traditionally, research on probiotics has primarily focused on lactic acid bacteria and bifidobacteria; however, there is a growing global interest in incorporating yeast as a probiotic supplement. Notably, yeast species such as Saccharomyces, Candida, Debaryomyces, Yarrowia, and Kluyveromyces have been identified for their probiotic potential. These probiotic yeasts are commonly introduced into dairy products, including kefir, yogurt, kumis, and cheese. However, the compatibility of probiotic yeasts with dairy matrices, as well as the factors influencing their viability and functionality, remains a critical area of study. Ongoing research focused on exploring techniques to enhance yeast viability during processing, given that different strains may exhibit varying survival rates and probiotic properties. Consequently, probiotic yeasts represent a promising avenue for augmenting the health benefits of dairy products. This development prompts essential discussions regarding selecting suitable probiotic yeasts for specific dairy applications. This paper comprehensively examines the historical discovery, types, properties, and applications of probiotic yeasts in dairy products. It aims to shed light on their health effects while addressing the challenges associated with selecting the appropriate probiotic yeast to optimize the enhancement of dairy products.

Graphical Abstract

Introduction

Since ancient times, probiotic yeasts have played a significant role in the food and beverage fermentation industry. The concept of probiotics gained prominence in the early twentieth century, sparking ongoing research into the potential of these microorganisms. Among the well-studied probiotic yeasts, Saccharomyces boulardii has been particularly noted for its therapeutic properties and health benefits (Ansari et al., 2023). In addition to Saccharomyces boulardii, other yeast species such as Kluyveromyces lactis, Candida milleri, Debaryomyces hansenii, and Yarrowia lipolytica have been explored, especially in the dairy industry, for their potential probiotic attributes and ability to thrive in various dairy products (Pourjafar et al., 2023). Dairy products, including yogurt, cheese, fermented milk (e.g., kefir and cultured buttermilk), and kumis, provide an ideal environment for the incorporation of probiotic yeasts. These products not only offer favorable conditions for yeast growth but also provide a unique opportunity to enhance gut health and improve their nutritional profiles. For instance, probiotic yeasts can enhance the content of proteins, vitamins (such as B12), and minerals (such as calcium and magnesium) in these products, contributing to better nutrient absorption and protein digestion. Additionally, probiotic yeasts may aid in the production of anti-inflammatory compounds and boost the immune system, offering substantial health benefits (Ansari et al., 2023). When selecting probiotic yeasts for dairy applications, several critical criteria must be considered, such as their ability to survive and remain viable, their safety for consumption, adhesion and colonization capabilities, acid and bile tolerance, and antimicrobial activity. These factors are essential in ensuring the efficacy and safety of probiotic yeasts in final dairy formulations (Gürkan Özlü et al., 2022). It is important to note that not all fermented foods qualify as probiotic-containing products, as some processes may remove or inactivate the probiotic strains, and only specific strains sufficiently characterized at the molecular level can be classified as probiotics (Soemarie et al., 2021).

The future of probiotic yeast incorporation in the dairy industry holds considerable promise. Researchers are continuously exploring innovative ways to maximize their health benefits, develop novel products, personalize nutrition, and achieve sustainability in production processes. By leveraging technological advancements, probiotic yeasts are poised to contribute significantly to the dairy industry's growth and innovation and meet consumers' evolving preferences in an increasingly dynamic market.

History of yeast and probiotic yeast exploration

Ancient origin of yeasts

Yeasts are single-celled fungi from the kingdom of Fungi and are widely utilized in the food and medicinal industries. These microorganisms are primarily classified into two groups: ascomycetes and basidiomycetes. Each group encompasses a diverse range of species with significant applications in both sectors. Under specific environmental conditions, ascomycetous yeasts can produce ascospores within their cellular structure, while basidiomycetous yeasts are capable of forming external spores. This reproductive capability contributes to their adaptability and utility in various applications.

The historical use of yeasts in the preparation of beverages and foods dates back approximately 5,000 years, underscoring their long-standing role in human culinary practices. Yeasts have played a crucial role in the fermentation of food and beverages throughout history. Ancient civilizations likely discovered the fermentative properties of yeast through observation and experimentation, leading to the development of various fermented products that are integral to many cultures today (Marullo & Dubourdieu, 2022). One of the key roles of yeast in fermentation is the conversion of sugars into carbon dioxide and alcohol through a process known as alcoholic fermentation. This process is extensively utilized in the production of alcoholic beverages, such as beer and wine. The yeast primarily responsible for this fermentation is Saccharomyces cerevisiae (Marullo & Dubourdieu, 2022). In addition to alcoholic fermentation, yeast also participates in other fermentation processes, such as bread fermentation. During bread making, yeast helps leaven the dough by producing carbon dioxide, which causes the bread to rise in volume. This has been a common practice in baking for centuries (Castro et al., 2022). The ancient Egyptians, Greeks, and Romans are known to have utilized fermentation in the production of various alcoholic beverages. Throughout history, the understanding and control of fermentation processes have evolved significantly, leading to the development of diverse traditional food and beverage products. The fermentation techniques employed by these ancient civilizations laid the groundwork for modern practices, influencing the production of alcoholic drinks and other fermented foods. As societies progressed, the refinement of fermentation processes contributed to the enhancement of flavors, preservation methods, and nutritional profiles of these products, demonstrating the enduring significance of fermentation in culinary traditions. This historical context underscores the importance of fermentation not only as a method of food production but also as a cultural practice that has shaped dietary habits and food systems across different regions (Cuamatzin-García et al., 2022). In modern times, the use of yeast in fermentation has expanded to encompass industrial-scale production of a diverse array of products. This includes not only alcoholic beverages and bread but also various fermented foods such as yogurt, sauerkraut, and soy sauce. Yeast remains a crucial microorganism in the food and beverage industry, contributing significantly to both the flavor and preservation of these products (Romano et al., 2022).

Discovery of probiotics

Throughout history, the exploration of probiotics has predominantly employed higher-level methodologies. In this approach, microorganisms that are abundant in healthy individuals, as opposed to those found in altered health states, have been considered potentially beneficial. These microorganisms were subsequently subjected to further investigation to assess their potential health benefits when administered to humans. In the last century, this observational method has led to the discovery of various potential probiotics, notably including strains of Bifidobacterium spp. and Lactobacillus spp (O’Toole et al., 2017). Elie Metchnikoff proposed an alternative empirical approach to the exploration of probiotics, based on the correlation between the intake of fermented foods and their beneficial health effects. This approach focused on identifying microorganisms that were abundant in fermented foods and exploring their potential probiotic properties when administered to humans. With the advancement of molecular techniques, our ability to identify novel probiotic candidates has expanded significantly. These techniques have proven particularly valuable for microorganisms that were previously difficult to cultivate due to their specific and demanding growth conditions. Examples of such probiotic candidates include Faecalibacterium prausnitzii and Akkermansia muciniphila. Alongside the top-down approach pioneered by Metchnikoff, recent advances in gut microbiome research have given rise to bottom-up probiotic discovery strategies. These strategies, reminiscent of those employed in drug discovery, encompass two distinct development pathways: phenotypic and target-based discovery (Suez et al., 2019). The phenotypic approach relies on the evaluation of probiotic effects through screening in vitro and ex vivo cell cultures, as well as the utilization of animal models that feature various immune, neuronal, metabolic, or microbial readouts. An illustrative example of this method is the development of the Lactobacillus rhamnosus JB-1 strain. This particular strain was meticulously selected through in vitro screenings and subsequently confirmed through in vivo studies. In these studies, mice exhibited decreased corticosterone release, altered central expression of gamma-aminobutyric acid receptors, and improved stress-related social and exploratory behaviors in models simulating anxiety and depression. However, it is important to emphasize that these positive effects were not replicated in human subjects (Suez et al., 2019). Conversely, the target-based discovery approach relies on identifying potential probiotic candidates primarily through in silico predictions of their ability to produce molecular effectors. These effectors are anticipated to influence crucial host or microbial pathways involved in health and disease. The in silico predictions necessitate the application of multi-omics techniques, including genomics, transcriptomics, metabolomics, and proteomics. These techniques may be further enhanced by metabolic reconstruction, which evaluates the metabolic capacities of the screened microorganisms (Kelly et al., 2017; Lucas et al., 2019).

Definition and characteristics of probiotic yeasts

Probiotics, defined as live microorganisms, can have beneficial impacts on human and animal health when consumed in sufficient quantities. Probiotic foods enhance the engagement and activity of indigenous microflora within the host system (Sanders et al., 2018). The consumption of probiotic foods contributes to the preservation of beneficial microflora, influencing the immune system, digestion, metabolism, and communication between the gut and the brain (Ugras et al., 2024). Probiotics provide defense against harmful bacteria and play a crucial role in maintaining overall health (Wels et al., 2011). Probiotic yeasts constitute a specific group of microorganisms that, confer health benefits to the host when consumed in adequate amounts. Distinguished from probiotic bacteria, these yeasts belong to the fungal kingdom, with Saccharomyces and Candida species being the most extensively studied (Staniszewski & Kordowska-Wiater, 2021). The suitability of these microorganisms for probiotic applications arises from their distinctive traits. Notably, probiotic yeasts exhibit high endurance in acidic conditions within the gastrointestinal tract, ensuring their survival through the stomach and successful arrival in the intestine, which are vital for potential health effects (Alkalbani et al., 2022a, 2022b). Moreover, the ability of probiotic yeasts to adhere to intestinal epithelial cells enhances their colonization and persistence in the gut. This adhesive capability is attributed to specific surface proteins and glycoproteins present on the yeast cell membrane (Staniszewski & Kordowska-Wiater, 2021). Upon survival and adherence, probiotic yeasts exhibit immunomodulatory effects by stimulating cytokine production and enhancing immune cell activity. Additionally, they demonstrate antimicrobial activity against pathogenic microorganisms through the production of compounds such as organic acids, hydrogen peroxide, and antifungal peptides.

Probiotic yeasts play a significant role in various food industries due to their beneficial effects on human health and food quality. Unlike probiotic bacteria, which are commonly found in dairy products like yogurt and fermented milk, probiotic yeasts offer distinct advantages and applications in different food products (Chapot-Chartier & Kulakauskas, 2014).

Each probiotic yeast strain requires specific growth conditions to thrive and exert its probiotic effects. For instance, Saccharomyces boulardii, known for its ability to inhibit harmful bacteria in the intestines, thrives at temperatures between 20–37 °C and within a pH range of 4–6 (Gibson et al., 2017). On the other hand, Kluyveromyces lactis contributes to dairy products such as butter by producing beneficial dairy enzymes, thereby enhancing their quality and performance (de Souza et al., 2022).

In the context of dairy products, understanding the distinction between alcoholic fermentation, facilitated by yeasts, and lactic acid fermentation, primarily driven by lactic acid bacteria, is crucial. Alcoholic fermentation contributes to the flavor profile and texture of bakery products and cakes, whereas lactic acid fermentation in dairy products like yogurt leads to the characteristic tangy flavor and enhanced microbial stability (Gibson et al., 2017).

In conclusion, probiotic yeasts present promising potential for enhancing human health. Their ability to survive in the gastrointestinal tract, adhere to intestinal cells, exert immunomodulatory effects, and demonstrate antimicrobial activity make them appealing candidates for probiotic applications. Nevertheless, careful selection and characterization of strains are imperative to ensure their efficacy and safety in dairy products.

Probiotic yeast research

Although most research on probiotic microorganisms' properties has focused on bifidobacteria and lactic acid bacteria, there is a growing recognition of the importance of incorporating yeast as a probiotic food supplement (Fleet & Balia, 2006). In recent years, the advancement of molecular phylogenetic science has facilitated the reclassification of numerous yeast species. The typing process is accomplished through the utilization of species-specific polymerase chain reactions (PCR) in an academic context (Czerucka et al., 2007). In modern times, numerous advances have been documented regarding understanding the advantageous characteristics and operational procedures of specific yeast strains (Czerucka et al., 2007). The use of yeast in the dairy industry has been the subject of ongoing research, particularly in the context of its potential probiotic properties and benefits for dairy production. Yeasts, such as Saccharomyces cerevisiae and Saccharomyces boulardii, have been studied for their effects on dairy production efficiency, milk quality, and animal health. Research has shown that yeast supplementation can enhance the nutritional digestibility and efficiency of microbial protein nitrogen production, boost milk yield, and enhance milk quality in dairy animals (Alvarez-Martin et al., 2008). In addition to their potential benefits for dairy production, yeasts have been recognized for their therapeutic properties, particularly in normalizing the intestinal flora and treating a range of gastrointestinal conditions. The use of yeasts, such as acidophilus yeast milk, kefir, koumiss, and laban, in dairy products has historical significance, as these products incorporate yeasts in their starter cultures, along with lactic acid bacteria and acetic acid bacteria, to facilitate the fermentation of milk (Lama & Tamang, 2022). Furthermore, yeasts can utilize organic acids and thrive in the gastrointestinal milieu, making them suitable for employment in the food industry. The selection of potentially probiotic yeasts for dairy products involves evaluating their ability to survive within the gastrointestinal environment and assessing their possession of advantageous functions. Ongoing research aims to identify additional yeast strains with noteworthy probiotic potential for use in the food industry (Alkalbani et al., 2022a, 2022b). In Indonesia, extensive research has been carried out on yeast as a possible probiotics for human health. Isolated strains such as C. stellimalicola and Cyberlindnera (Pichia) jadinii from Dadih have demonstrated the capacity to improve lactate degradation during fermentation (Al Halim et al., 2024). Another yeast, C. famata, isolated from Kefir, was found to increase protein concentration and acidity in Kefir samples (Suriasih et al., 2012). Additionally, C. guilliermondii from Danke, a milk-based fermented food, has shown probiotic characteristics, such as acid and bile salt resistance, high coaggregation activity, and antibacterial effects against pathogens. Yeast strains such as Saccharomyces sp. isolated from Budu, a fermented fish food, exhibit survival in gastric juice and bile acids, as well as hydrophobicity and the ability to inhibit bacterial pathogens (Marlida et al., 2021). Furthermore, yeast strains such as Kluyveromyces sp., Pichia sp., and Saccharomyces sp. from Local Siam orange juice fermentation have shown potential probiotic properties by surviving in acidic conditions and inhibiting pathogenic E. coli (Astuti et al., 2023). Finally, the local strain C. orthopsilosis isolated from fermented fish (WadiPapuyu) has shown promise as a probiotic due to its tolerance to low acidity (Soemarie et al., 2022). In a previous study, 10⁷Pichia kudriavzevii strains were isolated from sourdough, shalgam, tarhana, artisanal Tulum cheese, and yogurt. These strains were identified through DNA fingerprinting using the iPBS-PCR method, followed by technological and probiotic assessments. They were deemed particularly promising in terms of technological attributes, demonstrating resilience under various challenging growth conditions. Furthermore, these strains exhibited probiotic properties comparable to those of commercial strains, including S. cerevisiae var. boulardii MYA-796. The findings indicated that P. kudriavzevii 5S5 displayed notable in vitro probiotic characteristics, such as survival in conditions mimicking the human gastrointestinal tract, adherence to intestinal cell lines, and elevated hydrophobicity. Consequently, this strain appears to be a highly suitable candidate for the production of functional fermented food products (Kahve, 2023). A study explored the probiotic effects of indigenous Debaryomyces hansenii sourced from dry fermented sausages and its potential in the meat industry. The researchers isolated this yeast species from dry fermented sausages and demonstrated its probiotic effects in animal models, suggesting possible probiotic activity in humans. Additionally, the study reported on the functional abilities of food yeasts, including their anti-inflammatory, antioxidant, antimicrobial, antigenotoxic, and immune-modulating properties. The findings from this study support the use of dry fermented sausages as vehicles for delivering molds and potentially probiotic yeasts, such as D. hansenii, to consumers. The approval of this application highlights the growing recognition of the potential health benefits associated with incorporating probiotic yeasts into fermented meat products (Álvarez et al., 2023). Unconventional yeasts, sourced from diverse environmental outlets and commonly present in mixed fermentation processes within the beverage industry where the microbial community is often not fully characterized were the focus of this study. In this research, unconventional yeasts isolated from fruits, leaves, and fermented beers were combined, and their species were identified through polymerase chain reaction (PCR) techniques. The yeasts were evaluated for their growth potential under various pH levels, temperatures, and organic acid concentrations. To assess the probiotic capabilities of these strains, in vitro tests were conducted to evaluate safety. These tests aimed to assess several key safety parameters, including hemolytic activity to ensure that the strains do not cause red blood cell lysis, which would indicate potential pathogenicity; antibiotic susceptibility to determine whether the strains carry any antibiotic resistance, which is crucial for ensuring they do not contribute to the spread of antibiotic-resistant genes; cytotoxicity using cell culture assays to check for any toxic effects on mammalian cells; and pathogenicity tests, including assessments for any virulence factors that might indicate a risk to human health. Additionally, the probiotic yeasts were evaluated for their ability to survive and grow under gastrointestinal conditions, such as low pH and the presence of bile salts, to ensure they can effectively colonize the host and exert their beneficial effects (Hatoum et al., 2012; Kumura et al., 2004; McFarland, 2010). Additionally, the study evaluated antimicrobial activity, interactions with food-spoiling microorganisms, automated collection, and survival under simulated gastrointestinal conditions. Among the 20 isolates, Pichia kluyveri LAR001, Hanseniaspora uvarum PIT001, and Candida intermedia ERQ001 were selected for further investigation. Notably, P. kluyveri LAR001 was the only strain that demonstrated tolerance to pH 2.5. These unconventional yeasts exhibited probiotic potential, suggesting promising applications in the fermentation of beer (Piraine et al., 2023).

In general, numerous studies have focused on the discovery and utilization of potentially probiotic yeasts, some of which have been mentioned above.

Probiotic yeasts in dairy products

Several probiotic yeasts can be used in dairy products, as illustrated in Fig. 1.

Fig. 1

Probiotic yeasts used in dairy products

Saccharomyces cerevisiae

Saccharomyces cerevisiae, commonly known as baker's or brewer's yeast, has broad applications in baking, brewing, and biotechnology (Karathia et al., 2011). In the realm of baking, it plays a significant role in leavening bread and various baked products. This yeast ferments the sugars present in the dough, resulting in the production of carbon dioxide gas, which causes the dough to expand and imparts the characteristic texture and flavor of bread (Heitmann et al., 2018). In the brewing industry, Saccharomyces cerevisiae is pivotal in the production of beer, wine, and other alcoholic beverages. Throughout the fermentation process, this yeast metabolizes sugars, transforming them into alcohol and carbon dioxide. This transformative action is responsible for both the alcoholic content and carbonation found in these beverages (Türker, 2014). Beyond brewing, Saccharomyces cerevisiae has widespread utility in biotechnology and research. It serves as a model organism for investigating the intricacies of eukaryotic cell biology and genetics. Scientists have conducted extensive studies on the genetic makeup and physiological functions of this fungus, rendering it an invaluable tool for a wide array of scientific applications (Walker & Stewart, 2016). In addition to its primary applications, Saccharomyces cerevisiae is harnessed as a nutritional supplement due to its abundant nutrient content, which includes B vitamins and minerals. It is commonly used as nutritional yeast to season or enhance the flavor of vegan and vegetarian dishes (Pimenta et al., 2009). Recently, Saccharomyces cerevisiae has emerged as an exceptionally versatile and extensively researched yeast species found in certain probiotic supplements and some foods, where it serves as a beneficial microorganism that can potentially promote digestive health. Its diverse range of industrial, scientific, and culinary uses highlights its capacity to ferment sugars and convert them into valuable products, thus establishing its importance across various fields, including the food and beverage industry (Walker & Stewart, 2016). In the food industry, Saccharomyces cerevisiae is essential for the production of bread, beer, and wine, leveraging its fermentation capabilities. In pharmaceuticals, it is used to produce bioactive compounds and vaccines. Additionally, in biotechnology, it serves as a model organism for genetic studies and is employed in the production of biofuels and bioplastics (Nevoigt, 2008; Parapouli et al., 2020). Its ability to be genetically engineered makes it an invaluable tool for research and development across multiple scientific disciplines.

Saccharomyces boulardii

Saccharomyces boulardii, a yeast strain, was first isolated in the 1950s in Indochina from lychee fruit and has since been recognized for its prophylactic and therapeutic roles in managing various diarrheal disorders. This non-pathogenic yeast is noted for its potential to alleviate diarrheal symptoms (Wang et al., 2024). Extensive research has demonstrated its efficacy in humans, leading to its classification as a medicinal yeast. S. boulardii is commonly employed as a supportive treatment for gastrointestinal diseases that arise from the administration of antibiotics. The yeast exhibits several characteristics that endorse its use as a probiotic. It withstands the conditions of the gastrointestinal tract, with an optimal growth temperature of 37 °C. Additionally, S. boulardii has shown the ability to inhibit the growth of pathogens both in vitro and in vivo. Unlike bacterial probiotics, which are prokaryotic, S. boulardii is a eukaryotic organism (Sazawal et al., 2006). The initial identification of the hemiascomycete genus Saccharomyces included the recognition of a distinct species. Further investigations in 1994, utilizing electrophoretic karyotyping and multivariate analysis of polymorphisms detected through pulsed-field gel electrophoresis (PFGE), confirmed that S. boulardii is a separate species from Saccharomyces cerevisiae. The latter is a yeast species widely used in scientific research and in the production of bread, beer, and wine.

Kluyveromyces lactis

Kluyveromyces lactis (K. lactis) has emerged as a prominent candidate for research within the Kluyveromyces genus. Initially, this species was utilized for investigations into lactose metabolism; however, it has since evolved into a model organism for studying unconventional yeasts (Jacques & Casaregola, 2008; Spohner et al., 2016). K. lactis is widely employed in industrial applications, primarily due to its specific properties that make it suitable for such purposes, including its efficient metabolism of lactose and its ability to produce high yields of recombinant proteins (Holyavka et al., 2018). Additionally, K. lactis has been recognized as a Qualified Presumption of Safety (QPS) and has been classified as Generally Recognized as Safe (GRAS) by regulatory authorities in the United States and the European Union. This acknowledgment stems from the yeast's extensive use in the dairy industry and its established safety record within the broader community. These characteristics render K. lactis inherently suitable for the production of proteins intended for food-grade consumption and pharmaceutical applications (Wagner & Alper, 2016).

Kluyveromyces marxianus

In recent years, the yeasts K. marxianus and K. lactis have garnered significant research interest due to their beneficial features and unique industrial applications. These traits include their ability to consume large amounts of sugars, release lipid-decomposing enzymes, and grow more rapidly than other eukaryotic cells, which enables them to produce ethanol through fermentation (Lourens-Hattingh & Viljoen, 2001).

While K. marxianus has not received as much attention as K. lactis, it possesses considerable biotechnological potential. For instance, it can be utilized in the production of valuable bioethanol from whey and the generation of important enzymes within the food industry (Lourens-Hattingh & Viljoen, 2001). The increasing consumer demand for biologically synthesized molecules across various sectors, including the food industry, has created opportunities to explore and leverage the potential of K. marxianus for diverse industrial applications. This yeast is capable of fermenting lactose found in whey to produce bioethanol, a process attributed to its efficient lactose fermentation and high ethanol yield (Fonseca et al., 2008). Additionally, K. marxianus is employed in the production of various enzymes with applications in the food and pharmaceutical industries, including beta-galactosidase, invertase, and proteases. These enzymes are essential for the production of lactose-free milk, sweets, and infant formulas (Guimarães et al., 2010). Moreover, K. marxianus is capable of producing biopolymers such as polylactic acid (PLA), which are used in biodegradable packaging. It can also be employed to produce organic acids, including lactic acid and acetic acid, which have widespread applications in the food, pharmaceutical, and chemical industries (Lane & Morrissey, 2010). Additionally, K. marxianus is involved in the production of aromatic and flavor compounds such as esters and various alcohols, which are significant in the food and fragrance industries(Yamada et al., 2010). In summary, K. marxianus, with its unique capabilities and high potential, holds promise for various industrial applications, including bioethanol production, enzyme production, single-cell protein production, biopolymer production, organic acid production, and the synthesis of flavor and aroma compounds. These applications are increasingly important due to the rising demand for bio-based and natural products across different industries.

Debaryomyces hansenii

Debaryomyces hansenii, an unconventional yeast species within the Hemiascomycetes class, is ubiquitous across a wide range of environments, including saline water, food products, fruits and even the human gut (Jeong et al., 2022). It is renowned for its remarkable ability to withstand harsh conditions, exhibiting tolerance to extreme cold (cryo-tolerance), dryness (zero tolerance), and high salinity (halotolerance), This resilience enables it to thrive even in environments with exceptionally high salt concentrations, reaching up to 4 M NaCl (Nalabothu et al., 2023). D. hansenii plays a significant role in the production of surface-ripened cheeses and dry-aged beef, contributing to the unique flavor profiles by generating branched-chain aldehydes and alcohols. These compounds create a distinct aroma profile not achieved with other yeast species like Yarrowia lipolytica and Saccharomyces cerevisiae (Sørensen et al., 2023). Despite the limited number of human infection cases mistakenly attributed to D. hansenii or human-associated strains, its extensive use in food-related applications and minimal associated health risks have led to the European Food Safety Authority bestowing it with Qualified Presumption of Safety (QPS) status. Additionally, beyond its role in fermented food production, D. hansenii has been utilized in various biotechnological procedures. These include the biodegradation of pollutants, the production of bioethanol, and the synthesis of valuable enzymes (Castilleja et al., 2017). D. hansenii is particularly effective in the biodegradation of saline and alkaline wastewater, making it a valuable organism for environmental biotechnology applications. Furthermore, its ability to ferment glycerol into ethanol highlights its potential in biofuel production (Bessadok et al., 2022). The yeast is also employed in the production of enzymes such as lipases and proteases, which have applications in the detergent, leather, and dairy industries (Castilleja et al., 2017). Therefore, D. hansenii, with its versatile biotechnological applications and contributions to flavor enhancement in food products, stands out as a valuable microorganism in both industrial and environmental biotechnology (Jeong et al., 2022). In controlling undesired microorganisms’ proliferation in fermented foods, sausages, and olives (Jeong et al., 2022), D. hansenii showcases its versatility and potential across different domains. Notably, it generates mycotoxins effective against pathogenic Candida species. Moreover, its metabolic capability to utilize D-xylose has been harnessed for the production of xylitol from D-xylose and sugarcane bagasse hemicellulose (Prakash et al., 2011). Recent studies have explored D. hansenii strains as potential probiotics for fish, leveraging their antimicrobial and immunostimulatory effects in aquaculture (Angulo et al., 2019). Additionally, D. hansenii strains exhibit promise as human probiotics, because they induce higher levels of IL-10/IL-12 secretion in human dendritic cells (hDCs) compared to Saccharomyces boulardii, commonly used as a yeast probiotic for preventing and treating gastrointestinal disorders (Ochangco et al., 2016). The evolving role of D. hansenii within the gut microbiota across different life stages is worth nothing. While predominant in the neonatal gut during breastfeeding, its abundance diminishes post-weaning as S. cerevisiae becomes relevant (Schei et al., 2017). Genetically, D.hansenii displays heterogeneity with significant genetic diversity (Moslehi-Jenabian et al., 2010). This variability has led to the identification of different varieties, including D. hansenii var. fabryi, D. hansenii var. hansenii, and Debaryomyces tyrocola (Gori et al., 2011), This variability has led to the identification of different varieties, including D. hansenii var. fabryi, D. hansenii var. hansenii, and Debaryomyces tyrocola.

Yarrowia lipolytica

Yarrowia lipolytica is a remarkable oleaginous yeast known to thrive on diverse hydrophobic substrates and effectively store lipids, constituting as much as 40% of its cellular dry weight (Hapeta et al., 2017). This yeast species has garnered widespread attention due to its various applications across multiple industries. Yarrowia lipolytica has emerged as a reliable source of high-quality protein for livestock feed, presenting significant benefits in the agricultural sector (Bonfiglio et al., 2021).

Yarrowia lipolytica serves as an exceptional Biotechnological Manufacturing Platform for Organic Acids and Hydrophobic Compounds: This yeast serves as an exceptional biotechnological platform for producing organic acids, such as citric acid, and hydrophobic substances, including polyunsaturated fatty acids (PUFAs) and carotenoids. This capability creates opportunities for diverse biotechnological applications (Bonfiglio et al., 2021).

Demonstrating versatility, Yarrowia lipolytica has proven to be an effective host for producing a diverse array of pharmaceuticals, industrial proteins, and enzymes. This positions the yeast as a valuable asset in the field of biopharmaceutical research and development (Madzak, 2015).

Large-Scale Biofuel Production: yeast has been effectively utilized for large-scale biofuel production, highlighting indicating its potential as an eco-friendly alternative for generating energy (Beopoulos et al., 2009), and bioremediation applications due to its capacity to aid in the remediation of environmental pollutants and contaminants, reflecting is versatily across industrial sectors and its significant contributions to various biotechnological and environmental processes (Rao et al., 2013).

Candida milleri

Candida milleri, formerly known as Candida kefir, is a yeast species commonly found in various natural environments, including dairy products, fermented foods, and plant materials. It has gained recognition for its significant contribution to dairy fermentation, particularly in the production of kefir, a fermented milk beverage (Guzel-Seydim et al., 2011). In kefir production, Candida milleri plays a central role alongside lactic acid bacteria in the fermentation process. Traditionally, kefir grains containing a symbiotic culture of yeast and bacteria are introduced into milk. Within these grains, Candida milleri actively participates in fermentation, imparting kefir with its tangy flavor and effervescent qualities (Dimidi et al., 2019). Collaborating with lactic acid bacteria, including various Lactobacillus species, Candida milleri metabolizes lactose in milk, converting it into lactic acid and ethanol. This collaborative process results in the unique flavor and texture characteristic of kefir (Pillay, 2020). Notably, Candida milleri found in kefir and similar dairy products may offer potential probiotic benefits, promoting digestive health and enhancing the immune system by fostering a balanced gut microbiome (Shamekhi et al., 2020). Beyond kefir, Candida milleri is present in various other fermented dairy products and food items, which contributes to fermentation and improves taste and consistency (Rao et al., 2013). Identification of Candida milleri can be achieved through microbiological and molecular techniques, enabling its differentiation from other Candida species. However, rigorous control measures during production and storage are essential, as Candida milleri, like other yeast species, may be associated with food spoilage under specific conditions (Riesute et al., 2021).

Optimizing probiotic yeasts in dairy products: viability and functionality considerations

The compatibility of probiotic yeasts with various dairy products, along with the influence of processing conditions on their viability and functionality, is critical for the successful development of probiotic-enriched items. Factors such as acidity, fat content, and overall composition of dairy products significantly affect the survival and activity of probiotic yeasts.

For instance, the acidic nature of yogurt presents challenges for the survival of probiotic yeasts, necessitating careful selection of strains and processing parameters. Ongoing research aims to optimize strain selection and processing conditions to enhance the viability and functionality of probiotic yeasts, ultimately striving to deliver effective probiotics across a range of dairy products.

The successful production of probiotic dairy products hinges on several critical factors, including the compatibility of probiotic yeasts with different types of dairy products and the influence of processing conditions. Ensuring the effective application of probiotic yeasts in dairy products remains a central focus of ongoing research. This study area has concentrated on identifying and characterizing potential probiotic yeast strains sourced from both fermented dairy and non-dairy foods. Research efforts have also extended to evaluating the survival of these microorganisms under in vitro digestion conditions and their tolerance to bile salts (Alkalbani et al., 2022a, 2022b). The challenges associated with the poor survival of probiotic bacteria in yogurt, primarily linked to the product's low pH, have prompted investigations into the viability of dairy-associated yeasts in yogurt and related products. Furthermore, the probiotic properties of yeasts used in fermented dairy production have been scrutinized, particularly regarding their ability to withstand gastric conditions and reach the gut intact to fulfill their functional roles (Sørensen et al., 2023). Fermented dairy products, such as cheese, have gained attention due to the potential presence of beneficial compounds resulting from the metabolic activity of microbiota, including probiotics. This aspect has been explored more recently (Mogmenga et al., 2023). Research highlights the critical importance of selecting fermentable yeast strains capable of thriving in the specific conditions of dairy products, such as the acidity of yogurt or the fermentation process in cheese.

The viability of probiotic yeasts throughout the shelf life of dairy products is a key consideration for conferring health benefits. Researchers are actively investigating the interactions between probiotic yeasts and other microorganisms involved in dairy fermentation, as well as the influence of these interactions on taste and texture (Fernández et al., 2015). The compatibility of probiotics with various dairy matrices and other food products is crucial in the development of functional foods. Additionally, regulatory considerations add complexity to the utilization of probiotic yeasts in dairy products, as these regulations can vary significantly by region. The viability, functionality, and compatibility of probiotic yeasts can be influenced by the specific food matrix in which they are incorporated (Companys et al., 2020). This underscores the importance of understanding the interactions between probiotic yeasts and the components of dairy products (Companys et al., 2020).

In summary, ongoing research endeavors aim to optimize the selection of strains and processing conditions to increase the viability and functionality of probiotic yeasts, ultimately striving to deliver effective probiotics across a spectrum of dairy The viability, functionality, and compatibility of these materials can be influenced by the specific food matrix in which they are incorporated (Companys et al., 2020).

Here are some key considerations:

Compatibility of probiotic yeasts with dairy matrices (Table 1)

Table 1 Various dairy products that can contend probiotic

Dairy products are integral components of the human dietary regimen (Moayednia et al., 2009; Tamime & Marshall, 1997; Tamime & Robinson, 1999; Yerlikaya, 2014)., because of its diverse use of favorable physiological and taste agents.

Fermented dairy products are generated through the utilization of diverse fermentation techniques and/or conventional methods, particularly lactic acid fermentation, in conjunction with the incorporation of starter cultures. Although these processes produce products characterized by varied textures and aromas, their compositions are similar. Such processes yield products characterized by varied textures and aromas.

Recently, due to the expanded quest for healthy items and characteristic supplements, mature dairy refreshments have arrived in unique circumstances and are considered to have a critical effect on nourishment and human well-being (Tamime & Marshall, 1997).

Yogurt

The addition of probiotics, including lactic acid bacteria and yeasts, to yogurt enhances its health benefits and quality attributes. The acidic, semisolid nature of yogurt provides an ideal environment for the survival of these beneficial microorganisms (Olson & Aryana, 2022). Several factors, including pH, redox potential, acidity, and storage temperature, influence the viability of probiotics during yogurt storage. Refrigeration is widely recommended to maintain the efficacy of probiotics (Ferdousi et al., 2013). In addition to lactic acid bacteria, probiotic species such as Lactobacillus bulgaricus and Streptococcus thermophilus may be incorporated into yogurt cultures (Sfakianakis & Tzia, 2014). The incorporation of probiotics into yogurt results in functional foods with improved aroma, flavor, taste, and texture (Gkitsaki et al., 2024), These enhancements offer consumers multiple health benefits, including improved digestion, enhanced immune function, and a reduction in the severity of lactose intolerance. Such benefits arise from the ability of probiotics to maintain gut health, prevent gastrointestinal infections, and modulate the immune system (Castilleja et al., 2017; Fonseca et al., 2008). Specifically, Saccharomyces boulardii CNCM I-745 is a probiotic yeast strain that has been utilized in the production of synbiotic yogurt, which contains both probiotics and prebiotics. One study demonstrated that synbiotic yogurt could be produced by combining S. boulardii with inulin at various concentrations. The resulting yogurt was favorable in terms of quality and served as an effective carrier for the delivery of probiotic yeast (Sarwar et al., 2019). Another study investigated the growth and survival of S. boulardii in commercial bioyogurt environments, showing that this yeast strain can thrive in association with bioyogurt microflora (Lourens-Hattingh & Viljoen, 2001). The addition of probiotic yeast to yogurt has been shown to improve its chemical and rheological properties (Niamah, 2017). Thus, probiotic yeasts such as S. boulardii can be effectively used in yogurt production to provide health benefits, including improved digestion, enhanced immune response, and prevention of gastrointestinal disorders. It is important to note that the health benefits of this probiotic yeast depend on the specific strain used (Fig. 2).

Fig. 2

Production stages of yogurt

Milk

Positively influencing intestinal microbiota, probiotic strains may even exhibit anti-obesity effects by reducing body mass index. Researchers have conducted numerous studies to enhance these strains' survival by fortifying milk with diverse nutrients necessary for the growth of lactic acid bacteria (Khorshidian et al., 2020). Adding probiotic strains to milk is particularly important in developing functional dairy products, as they can significantly enhance the health benefits by contributing to gut health and boosting immune function. Additionally, incorporating yeasts into milk, alongside probiotics, can yield a functional food with enhanced quality attributes, including aroma, flavor, taste, and texture (Hadjimbei et al., 2022). This combination not only meets consumer demands for taste and quality but also offers significant health benefits. Ongoing research continues to explore the optimal conditions for probiotic survival and functionality in dairy products (Kaur et al., 2022).

Cheese

Incorporating probiotics into cheese presents various challenges due to factors such as low pH, low salt content, and extended aging periods. Certain cheese varieties may not support the survival of probiotics as effectively as other dairy products. However, many soft and hard cheeses—including Swiss, Provolone, Gouda, Cheddar, Edam, Gruyère, Feta, Caciocavallo, Amantal, and Parmesan—are likely to contain live microorganisms with potential probiotic activity. Cheeses are typically aged or produced from raw, unpasteurized milk, and raw cheese can be made from various milk sources, with Cheddar, Feta, and Gouda being among the most common varieties. Provolone, Edam, Caciocavallo, Amantal, and Gruyère are also recognized for their live microorganism content (Gardiner et al., 1998). Yeasts play a vital role in the production of traditional ripened cheeses, significantly contributing to their characteristic taste and appearance. Alongside other microorganisms, yeasts can form complex biofilms on the surfaces of young cheeses, particularly in mature varieties such as Gruyère, Tilsit, Reblochon, and Munster, which rely on yeasts for their distinctive characteristics. Additionally, yeasts, including those found in Camembert, Stilton, and Tomme de Savoie, are crucial to the fungal ecosystem of mold-ripened cheeses. In the initial stages of cheese production (Fig. 3), specific fermenting yeasts can thrive within the cheese, generating ethanol and carbon dioxide. This process is particularly significant in acid-curd cheeses like German Harzer and Czech Olomoucké tvarůžky, where rapid yeast fermentation occurs in a controlled environment known as a "sweat room." Recently, there has been a growing trend toward using yeasts as supplementary cultures in cheesemaking, especially for rind and blue-veined cheeses. These new cultivars offer unique characteristics, such as fruity flavors, bitterness, inhibition of undesirable molds like Mucor spp., and improved texture. One of the primary contributions of yeasts to cheese ripening is the increase in pH on the cheese surface due to the metabolism of lactate into carbon dioxide and water. Once lactate is depleted, yeasts often utilize amino acids as an energy source, resulting in the production of significant amounts of ammonia. Many yeasts also exhibit proteolytic activity, releasing amino acids and lipolytic activity, which breaks down fats (Fröhlich‐Wyder et al., 2019).

Fig. 3

Production stages of cheese

To gain a more detailed understanding of the specific influence of yeasts on cheese quality, four important yeast species have been described in more detail in the literature. Three of these species, D. hansenii, K. marxianus, and G. candidum, are commonly cultivated as commercial cultures for ripening, while the fourth species, Y. lipolytica, is usually intentionally cultivated during the cheesemaking process(Pham et al., 2017).

In conclusion, yeasts play a crucial role in cheese maturation, impacting flavor development, and contributing to the unique characteristics of various types of cheeses. The use of commercial yeast cultures and the increasing popularity of auxiliary yeast cultures have given cheesemakers more control over the ripening process and increased the overall quality of the final product(Fröhlich‐Wyder et al., 2019). Understanding the specific interactions and contributions of different yeast species is essential for optimizing cheesemaking practices and obtaining desirable flavor profiles.

Kefir

Kefir is a naturally fermented milk product produced from kefir seeds or mother cultures derived from kefir grains. It can be manufactured using both traditional methods and industrial processes, employing various types of milk (Leite et al., 2013; Upendra et al., 2021; Yerlikaya, 2014). The steps involved in traditional and industrial kefir production are illustrated in Fig. 4. Kefir grains consist of lactic acid bacteria (LAB) and various yeast species that are inoculated with casein and complex sugars within a polysaccharide matrix. Additionally, acetic acid bacteria (AAB) and non-lactose-fermenting yeasts are also present in kefir grains (Upendra et al., 2021). The microbial population of kefir grains represents a symbiotic community that cannot be synthesized artificially; pure cultures of the individual organisms do not spontaneously form when placed together in a controlled environment, such as a test tube. However, under appropriate conditions, kefir grains can be cultivated and propagated through traditional methods (Leite et al., 2013; Yerlikaya, 2014). The composition of the kefir microbiota varies according to the cultivation environment and production method (Gebre et al., 2023). While kefir naturally contains a diverse microbial population, the addition of specific probiotic strains, such as Lactobacillus acidophilus or Bifidobacterium bifidum, has been explored to enhance its functional properties. Studies have reported that supplementing kefir with probiotics can improve gut health, boost immune function, and provide anti-inflammatory effects(Bourrie et al., 2016). Furthermore, the addition of probiotics can improve the sensory and textural Furthermore, the addition of probiotics can enhance the sensory and textural properties of kefir, resulting in a creamier and more palatable product. Harmankaya (2023) demonstrated that kefir prepared with probiotic cultures exhibited increased viscosity and improved sensory scores, making it more appealing to consumers. The combination of kefir and probiotics also offers potential for developing functional dairy products with extended shelf life and superior health benefits compared to traditional kefir alone (Harmankaya, 2023).

Fig. 4

Production stages of kefir

Kumis

Kumis is a traditional fermented dairy product made from cow's milk, primarily consumed in both rural and urban areas of southwestern Colombia. While kumis is often associated with mare's milk and produced through fermentation involving lactic acid bacteria (LAB) and yeast, its preparation has historical roots among the ancient Scythians. In the fifth century BC, Herodotus noted, "The Scythians make kumis from mare's milk." The Scythians fermented mare's milk in wooden containers, keeping the process a closely guarded secret, as documented by Herodotus. This period marks the earliest recorded reference to the preparation of kumis. In the traditional method, kumis is a homemade beverage created through the spontaneous fermentation of whole raw milk over 2 to 3 days, depending on room temperature and the practices of the milk producers. The outcome of this fermentation process is a creamy, carbonated drink with a modest level of acidity and a low alcohol content of approximately 12%. It is typically stored at temperatures between 4 and 10 degrees Celsius and is best consumed within 3 days. Just before serving, sugarcane and cinnamon are added to enhance its flavor. The residual drink serves as an inoculum for the following day's preparation, as illustrated in (Fig. 5). In traditional fermented milk products such as Colombian kumis, the origin of fermentation is symbiotic, and the fermentation process depends on the functions of two distinct microbial lactobacilli, which have major fermentation effects on the aroma, texture, and acidity of the product and are also beneficial for human health (Tabanelli et al., 2016). The presence of yeasts is very important for ensuring the favorable properties of carbon dioxide and ethanol(Lyumugabe et al., 2014). Moreover, enterococci can also occur. As a fermentation product, Kumis contains live microorganisms, including lactic acid bacteria (LAB) and yeasts, which can have beneficial effects on gut health and overall well-being. Studies have shown that naturally fermented beverages like kumis can provide functional benefits due to the presence of live microorganisms. These microorganisms, through their metabolic activities, can positively influence the gut microbiota and contribute to improved digestive health. For instance, fermented dairy products are recognized for their potential to enhance gut flora balance and exhibit probiotic-like properties even without intentional probiotic strain addition(Abdul Hakim et al., 2023). Therefore, while kumis is traditionally valued for its sensory attributes and health benefits stemming from fermentation, it can be considered a functional fermented beverage with probiotic-like effects.

Fig. 5

Production stages of kumis

The benefit of yeast in dairy products (Table 1)

The versatility of yeasts, particularly Saccharomyces cerevisiae var. boulardii, enables their utilization as beneficial food additives and key components in symbiotic food products. This enhances the overall quality and nutritional value of various fermented foods. However, the interaction between yeast and lactic acid bacteria (LAB) can be complex and context-dependent, necessitating careful consideration in specific food production processes to ensure desirable outcomes. Saccharomyces cerevisiae secretes various growth factors, including amino acids and carbon dioxide, which promote the growth of Lactobacillus species. The release of carbon dioxide creates a localized micro-anaerobic environment that is preferred by Lactobacillus spp. (Suharja et al., 2014). Furthermore, yeast releases amino acids such as threonine, glutamine, alanine, glutamate, serine, and glycine, which support the growth of LAB and enable their survival in challenging environments (Ponomarova et al., 2017). In fermented milk products, Lactobacillus species break down lactose the primary sugar in milk, which S. cerevisiae cannot metabolize into galactose. This process provides a carbon source for yeasts. Additionally, the lactic acid produced by LAB can serve as a carbon source under aerobic conditions, encouraging certain species of Lactobacillus to generate increased quantities of kefiran. This food-derived biopolymer holds potential applications in both the food and biomedical industries (Sieuwerts et al., 2018).

Yeast strains, including potentially probiotic strains, can also be employed in the fermentation of grain products. For instance, Banik et al. reported the use of S. cerevisiae starter cultures for the biofortification of multigrain substrates in traditional Indian dishes. This fermentation process resulted in significant improvements in protein, fiber, and starch content while reducing the levels of antinutrients (Banik et al., 2020). Moreover, during fermentation, the antioxidant potential, total phenolic content, and total flavonoid content increased. Probiotic Saccharomyces strains, including S. cerevisiae var. boulardii, contribute to enhancing the nutritional value of plant-based foods by synthesizing folates and eliminating phytates and other antinutrients. The phytase enzymes produced by this yeast further enhance the bioavailability and absorption of essential minerals such as iron, zinc, magnesium, and phosphorus (Rajkowska & Kunicka-Styczyńska, 2012). Additionally, S. cerevisiae var. boulardii has demonstrated antimicrobial properties, enabling it to decompose mycotoxins such as aflatoxins, patulin, and ochratoxin A, thereby contributing to food safety (Liu et al., 2020). These various advantages suggest promising possibilities for improving the nutritional quality and safety of food products by incorporating functional properties from potentially probiotic yeasts.

Compatibility of probiotic yeasts with nondairy matrices

Plant-based beverages

Probiotics can be incorporated into plant-based beverages, including almond drinks, soy drinks, and coconut drinks. However, the suitability of these materials depends on several factors, such as pH and the presence of nutrients that support probiotic growth (Rasika et al., 2021). Soy drinks, rice drinks, and coconut drinks are commonly used as carrier matrices in the production of probiotic foods. Plant-based beverages are among the most popular ingredients for producing probiotic drinks. Despite their popularity, the nutritional profiles of plant-based milk substitutes are often unbalanced, and their taste profiles can limit consumer acceptance. Soy milk and nut-based drinks naturally contain some live microorganisms, such as Lactobacillus plantarum and various species of Bifidobacterium. These naturally occurring microorganisms contribute to the health benefits associated with these plant-based foods. However, to ensure the desired dosage and enhance the probiotic benefits, most manufacturers supplement these products with additional probiotic strains, such as Lactobacillus acidophilus NCFM, Lactobacillus casei Shirota, and Bifidobacterium bifidum BB-12 (Hill et al., 2014) These added microorganisms help achieve a balanced nutritional profile and improve the overall health benefits of the plant-based milk substitutes, such as enhanced digestion, strengthened immune function, and improved gut health (Harper et al., 2022). Additionally, many plant-based and fermented foods, such as kombucha, miso, tempeh, and sourdough bread, are excellent nondairy sources of microorganisms that confer general health benefits, such as providing antioxidants, supporting heart health, and reducing inflammation. These benefits are due to the presence of live cultures, bioactive compounds, and essential nutrients found in these fermented foods (Hill et al., 2014).

Impact of processing conditions

The impact of processing conditions is a critical factor in maintaining the viability and functionality of probiotic yeasts in food products and supplements. Various processing steps can influence probiotic survival, and careful consideration of these factors is essential for delivering effective probiotics. The following are key considerations related to the processing conditions:

Heat treatment

High-temperature processing, such as pasteurization, can reduce probiotic viability. To mitigate this issue, selecting heat-resistant strains and post-processing inoculation are effective strategies (Liu et al., 2014). Studies have shown that some Lactobacillus acidophilus strains, including Lactobacillus acidophilus NCFM, and certain probiotic yeasts such as Saccharomyces boulardii, are more heat-resistant and can maintain their viability and health benefits even after exposure to higher temperatures (Østlie et al., 2005). Therefore, the careful selection of probiotic strains and processing techniques is important for ensuring the viability of probiotics in food products and supplements.

Fermentation

The fermentation process itself can affect probiotic viability. Monitoring and controlling factors such as temperature and fermentation time are crucial for maintaining probiotic functionality (Lacroix & Yildirim, 2007). During fermentation, microorganisms progress through four main growth phases: lag, exponential, stationary, and death. The viability of probiotics can be affected by the duration of each phase as well as the temperature and pH of the fermentation process (Lacroix & Yildirim, 2007). Therefore, monitoring and controlling factors such as temperature and fermentation time are highly important for maintaining probiotic performance.

pH levels

pH levels in the food matrix can impact probiotic viability. Probiotics often thrive within specific pH ranges. Processing steps that alter the pH can therefore affect probiotic survival (Matouskova et al., 2021). Various food constituents, including additives, antimicrobial agents, and aromatic compounds, can exert both positive and negative effects on the viability of probiotic microorganisms. Antimicrobial compounds and bacteriocins, for instance, pose notable challenges to probiotic viability within the food matrix, particularly during storage (Dharmasena, 2012).

Therefore, careful selection of food matrices and processing techniques is important to ensure the viability of probiotics in food products and supplements.

Oxygen exposure

Oxygen exposure during processing can harm probiotics, as many probiotic strains are anaerobic and do not thrive in the presence of oxygen. Proper packaging and handling techniques that minimize oxygen exposure are essential (Akshat Talwalkar & Kaila Kailasapathy, 2004a). The interaction between oxygen and probiotic bacteria was studied by cultivating Lactobacillus acidophilus and various Bifidobacterium species. With different oxygen concentrations, the results showed that with increasing oxygen concentration, the viability of probiotics decreased (Akshat Talwalkar & Kasipathy Kailasapathy, 2004b). Some probiotic strains have higher oxygen tolerance than others, and some can even increase oxygen tolerance by direct exposure to oxygen (Khan et al., 2023). For example, vacuum packaging can reduce the oxygen content of a package, which can help preserve the viability of probiotics (Akshat Talwalkar & Kaila Kailasapathy, 2004a). Certain yeast probiotic strains, such as Saccharomyces boulardii and Kluyveromyces lactis, also undergo studies regarding their interaction with oxygen. Research often focuses on understanding how oxygen levels impact yeast growth, fermentation capabilities, and viability in probiotic formulations (Moslehi-Jenabian et al., 2010). Certain yeast probiotic strains such as Saccharomyces boulardii and Kluyveromyces lactis, also undergo studies regarding their interaction with oxygen. Research often focuses on understanding how oxygen levels impact yeast growth, fermentation capabilities, and viability in probiotic formulations. These investigations are crucial for optimizing conditions that maintain yeast probiotic viability and functionality during production and storage processes (Abid et al., 2022; Moon et al., 2020).

Freeze-drying and spray-drying

Freeze-drying and spray-drying are methods used to dehydrate probiotics into powdered products. The conditions during these processes can affect the viability of probiotics. Protecting probiotics during dehydration and ensuring proper storage after drying are critical (Misra et al., 2023). However, under in vitro digestion, freeze-dried probiotics had a lower level of viability than spray-dried probiotics. Despite freeze-drying micro-encapsulation being more effective than spray drying for protecting probiotic cells, the viability of all the microcapsules decreased over time (Gul & Atalar, 2019).

Post fermentation processing

Post-fermentation processing steps, such as cooling, mixing, or additional cooking, can impact probiotic survival and functionality. Care should be taken to minimize stress on probiotics during these steps. For instance, refrigeration can cause heat shock to probiotic cells, which can reduce their viability. Similarly, mixing can cause mechanical stress, affecting their survival (Rezvankhah et al., 2020). Overcooking can expose probiotic cells to high temperatures, further diminishing their viability. Proper storage and handling methods are also critical for maintaining the viability of probiotics (Mendonça et al., 2022).

Storage conditions

The storage conditions after processing also play a crucial role in maintaining probiotic viability. Temperature, humidity, and exposure to light can all impact probiotic effectiveness over time. Proper storage is essential for maintaining probiotic functionality throughout the product's shelf life. Probiotics should be stored in a cool, dry place and should not be exposed to temperatures above 21 °C (70°F) for extended periods, especially for long periods, unless they are specifically designed to withstand the conditions (Jannah et al., 2022). Probiotic supplements shipped with ice packs may require refrigeration, and most provide storage instructions on the label. Following these instructions is important to ensure that the probiotics remain viable (Fan et al., 2017).

In general, manufacturers should carefully consider processing conditions and select probiotic strains that can withstand the specific challenges posed by their chosen processing methods. Monitoring probiotic viability during processing and throughout the product's shelf life is essential to ensure that consumers receive the intended health benefits from probiotic-containing foods.

Micro-encapsulation for improved viability of probiotic yeasts

Micro-encapsulation techniques have been extensively researched to enhance the viability and functionality of probiotic yeasts in dairy products. These methodologies establish a protective barrier around yeasts, fortifying their resilience against various processing conditions. Diverse micro- or macro-encapsulation methods and materials have been explored to deliver bioactive ingredients into fermented milk products such as yogurt, cheese, and kefir. Encapsulation of bioactive compounds enriches dairy products, enhancing their stability and protective properties (Krasaekoopt et al., 2003).

Micro-encapsulation of probiotic cultures within the food matrix is recognized as an efficient technique for preserving and improving the nutritional and sensorial properties of foods by safeguarding the active compounds. In essence, manufacturers carefully consider micro-encapsulation techniques when developing probiotic-containing products to ensure that encapsulated probiotics deliver the intended health benefits to consumers. Micro-encapsulation refers to encapsulating probiotics at a microscopic level, typically within a size range of 1 to 1000 µm, which can offer enhanced protection and controlled release (Cook et al., 2012). On the other hand, encapsulation, in a broader sense, can refer to any size of encapsulation, including larger capsules that may not provide the same level of precision in release properties (Koh et al., 2022), elevate the viability and functionality of probiotic yeasts in dairy products, contributing. Micro-encapsulation of probiotics offers several advantages, including improved viability, increased stability, targeted release, masking of bitterness or off taste and consumer friendliness. Application of micro coatings protects probiotics from environmental stressors such as heat, moisture, oxygen, and acidity, which helps maintain probiotic cell numbers and increase viability during processing, storage, and consumption. Compared to nonencapsulated probiotics, microencapsulated probiotics are more stable, have a longer shelf life, and are suitable for products with a longer shelf life. The release of probiotics from microcapsules can be controlled by targeting specific sites in the gastrointestinal tract, increasing the chances of survival and colonization in the gut. Micro-encapsulation can also mask strong or bitter flavors associated with some probiotic strains and make the final product more palatable. Microencapsulated probiotics can be incorporated into a wide range of food and beverage products, including dairy products, baked goods, snacks, and supplements, without adversely affecting taste or texture, increasing consumer acceptability (Rajam & Subramanian, 2022; Shori, 2017).

The first step in micro-encapsulation is selecting a suitable coating material (Azar et al., 2020). According to its intended application and desired release characteristics, various materials can be used including gelatin, alginate, chitosan, and starch. Common coating materials for the encapsulation of probiotics include Milk-based proteins, zein, soy protein, collagen, and gelatin, which are widely used as food coating materials. Other coating materials that can be used for the micro-encapsulation of probiotics include cellulose, wax, thermoplastics, metal oxides, polyethylene glycol, polyvinyl alcohol, polyacrylate, and polystyrene (Chan & Zhang, 2005). While these materials are well-documented, it is important to highlight their unique properties and specific applications that make them suitable for different types of probiotics and encapsulation techniques. Milk-based proteins are also used as outer coatings for entrapped bacteria, as additives during dough preparation, and as additives in creams and fillings (Koh et al., 2022). Polisaccharides like alginate, chitosan, and starch are preferred for their biocompatibility and low toxicity (Pavli et al., 2018) and Polysaccharides alginate, chitosan, and starch are usually used as coating materials for the micro-encapsulation of probiotics due to their biocompatibility, biodegradability, and low toxicity drying and baking. The choice of coating material depends on various factors such as the specific needs of the application, the intended application, and the desired release properties. It is crucial to recognize that the choice of encapsulation method—whether micro- or macro-encapsulation—and the selection of coating material are significantly influenced by factors such as the target application, desired release properties, and the specific characteristics of the probiotic strain, all of which collectively determine the release profile and overall effectiveness of the encapsulated probiotics (Martín et al., 2015). Maltodextrin is the most used coating material for the micro-encapsulation of probiotics due to its low cost and availability (Koh et al., 2022). For example, in the case of fish oil micro-encapsulation, maltodextrin is the most suitable encapsulating material (Tirgar et al., 2015). This medium often contains the coating material in a liquid form (Misra et al., 2022). Zein, a corn protein, is known for its excellent film-forming properties and resistance to moisture, making it ideal for protecting probiotics in humid environments (Camelo-Silva et al., 2022). Soy protein provides a good balance between hydrophobic and hydrophilic properties, which enhances the stability of encapsulated probiotics during digestion (Gharsallaoui et al., 2012). Collagen, a structural protein, is valued for its biocompatibility and ability to form strong gels, making it suitable for use in functional foods and nutraceuticals. Gelatin, derived from animal collagen, is widely used due to its ability to form thermally reversible gels, which can protect probiotics during processing and storage (Potuk & Bayraktar, 2024).

These materials have been successfully employed in various studies to enhance the viability and functionality of probiotics. For instance, zein has been used to encapsulate Lactobacillus rhamnosus, demonstrating improved stability under simulated gastrointestinal conditions (Zhu et al., 2021). Similarly, soy protein has been effective in protecting Bifidobacterium longum during freeze-drying and storage (Oikonomopoulou & Krokida, 2017).

On the other hand, encapsulation methods include extrusion, spray drying, and coloration, other coating materials that can be used for micro coating include modified starch, cyclodextrin, cellulose, wax, thermoplastics, metal oxides, polyethylene glycol, polyvinyl alcohol, polyacrylate, and polystyrene (Reque & Brandelli, 2021). Encapsulation is a critical process in enhancing the stability and viability of probiotics during processing and storage.

Extrusion involves pushing the probiotic suspension through a small nozzle, where it forms droplets that solidify as they fall into a gel bath containing the coating material. This method is particularly useful for creating uniform microcapsules with a protective coating. Spray drying involves spraying probiotic cells in a heated drying chamber with a coating material. The heat causes the coating material to solidify around the probiotics and form microcapsules. This technique is widely used due to its efficiency and cost-effectiveness in producing large quantities of encapsulated probiotics. Coacervation involves complex chemical interactions between two or more substances in the presence of probiotics, resulting in the formation of a protective coating around them. After encapsulation, the microcapsules are typically dried and cured to harden the coating and ensure stability during storage (Liserre et al., 2007). Spray drying and extrusion are the most common micro-encapsulation techniques for probiotics due to their effectiveness in maintaining probiotic viability and functionality (Camelo-Silva et al., 2022).

Strain-specific variations in probiotic yeasts

Strain-specific variations refer to differences in characteristics, behavior, and effects among different strains of microorganisms, including probiotics. These variations are significant when selecting and using probiotic strains in various applications (Beck et al., 2022). Key aspects of strain-specific variations in probiotics include viability and survival, colonization and persistence, resistance to antibiotics, production of bioactive compounds, sensory attributes, and compatibility with food matrices. The following:

Viability and survival

Different probiotic strains may have different levels of viability and survival under certain conditions. Some strains are more robust than others and can withstand harsh environments, while others may be more sensitive to factors such as temperature, acidity, and exposure to oxygen (Grispoldi et al., 2020). Food matrix components that interfere with probiotics may negatively affect their ability to develop and survive (Casarotti et al., 2015). Laboratory tests can evaluate the viability of the probiotics in the product at the end of its shelf life and their survival in the gastrointestinal tract (Călinoiu et al., 2016).

Colonization and persistence

Probiotic strains may differ in their ability to colonize and persist in the gut. Some probiotics may adhere to the intestinal lining more effectively, allowing them to persist longer in the gastrointestinal tract than in the gastrointestinal tract (Roselli et al., 2021).

Resistance to antibiotics

Several probiotic strains may be more or less resistant to antibiotics, which is an important consideration when using probiotics alongside antibiotic treatments (Gueimonde et al., 2013). Resistance mechanisms involving identified antibiotic resistance genes (ARGs) include antibiotic evasion, antibiotic inactivation, and antibiotic target switching (Selvin et al., 2020).

Production of bioactive compounds

Probiotic strains can produce bioactive compounds, such as short-chain fatty acids (SCFAs) or antimicrobial substances, which can have specific health-promoting effects. These compound production capabilities can vary among strains (Indira et al., 2019).

Sensory attributes

Probiotic strains can contribute to the sensory attributes of food products, producing flavors, aromas, or textures characteristic of certain strains (Šertović et al., 2019).

Compatibility with food matrices

The compatibility of probiotic strains with different food matrices can vary. Some strains may thrive in dairy products, while others may perform better in nondairy or plant-based formulations (De Bellis et al., 2021).

Regulatory status & clinical evidence

Probiotics may have different regulatory statuses in various countries and regions. Some strains may be recognized as generally recognized as safe (GRAS) by FDA regulatory authorities, while others may require specific approval(Hoffmann et al., 2014). The European Union employs the Qualified Presumption of Safety (QPS) framework for safety(Wright, 2005). Different countries have diverse approval processes, leading to inconsistencies in regulatory guidelines(Arora et al., 2013). This lack of uniformity has prompted calls for harmonized global regulations (Arora & Baldi, 2015). Proposed solutions include a standardized approval process similar to drug applications, with exemptions for GRAS organisms(Arora & Baldi, 2015). The regulatory landscape is further complicated by probiotics' classification across various categories, including foods, dietary supplements, and pharmaceuticals. Developing consistent terminology and categorization is crucial for effective regulation and market development (Arora & Baldi, 2015).

Research and clinical evidence

The availability of research and clinical evidence supporting the efficacy and safety of specific probiotic strains can vary. A more established body of evidence is available for the health benefits of well-studied strains such as Lactobacillus rhamnosus GG and Bifidobacterium lactis BB-12 (Szajewska et al., 2016). Compared to other strains like Lactobacillus reuteri or Saccharomyces boulardii, which may have less extensive research backing their efficacy and safety(McFarland, 2010).

Strain-specific naming

To differentiate between probiotic strains, specific naming conventions are used, usually given by recognized cell culture houses. This includes the use of strain designations (e.g., Lactobacillus rhamnosus GG, Saccharomyces boulardii CNCM I-745) to specify the particular strain being used (Hill et al., 2016).

Due to these strain-specific variations, it is important for researchers, healthcare professionals, and manufacturers to carefully select and characterize probiotic strains based on their intended applications, scientific evidence, and desired outcomes. This ensures that the chosen strains align with the specific health goals and product requirements. Additionally, consumer education is essential to help individuals make informed choices about probiotic products and strains that may best suit their needs.

Section criteria for probiotic yeasts

When choosing a probiotic yeast for the dairy industry, several essential factors should be taken into account (Fig. 6):

Fig. 6

Essential factors in the selection of probiotic yeasts

Strain specificity

Careful consideration should be given to selecting a probiotic yeast strain that aligns with the desired health benefits and intended functionality. Different strains may have specific effects on the human body, emphasizing the importance of choosing the right strain for desired outcomes (Egea et al., 2023).

Survival and stability during processing and storage

The probiotic yeast must be able to endure and maintain stability under the processing and storage conditions typical in the dairy industry. This ensures that the beneficial properties of the yeast remain intact and that the material is effectively delivered to the consumer (Gao et al., 2021).

Probiotic attributes

The chosen yeast strain should exhibit key probiotic attributes, including the ability to adhere to the intestinal epithelium, withstand gastric acidity, and survive exposure to bile salts. These attributes are critical for yeast to successfully colonize the gut and confer health benefits (Gao et al., 2021).

Potential health effects

Evaluation of the potential health effects associated with the probiotic yeast strain is essential. Scientific studies and clinical trials should provide documented evidence of its positive impact on human health, such as improving digestion, enhancing immune function, or lowering the risk of specific diseases (Souza et al., 2021).

Safety

The selected strain must be nonpathogenic and nontoxic to ensure the safety of the probiotic yeast product (Sanders et al., 2010).

Adhesion and colonization

Yeast strains should be able to adhere to the intestinal epithelium and effectively colonize the gut (Ouwehand et al., 1999).

Acid and bile tolerance

The yeast strain should exhibit resilience and functionality in the acidic and bile-rich environment of the gastrointestinal tract (Shruthi et al., 2022).

Antimicrobial activity

Yeast strains should produce antimicrobial compounds that can inhibit the growth of pathogens (Gänzle, 2015).

Considering these factors meticulously, the dairy industry can choose a probiotic yeast that aligns with specific requirements, including strain specificity, survival, stability during processing and storage, probiotic attributes, and potential health effects.

Challenges in probiotic yeast production

Personalized nutrition and health risks

Incorporating probiotic yeasts into personalized dairy products can significantly enhance nutritional profiles and improve health outcomes. For example, strains like Saccharomyces boulardii have been shown to provide benefits such as improved gut health and enhanced immune response (Gürkan Özlü et al., 2022). However, there are potential health risks associated with yeast consumption. Excessive proliferation of yeasts in the gastrointestinal tract may lead to various health issues, including gastrointestinal discomfort, respiratory problems, and skin reactions. Some individuals with compromised immune systems might be at a higher risk of fungal infections or allergic reactions (Moslehi-Jenabian et al., 2010). Therefore, careful monitoring and management of these risks are essential to ensure the safety and efficacy of probiotic dairy products (Fleet & Balia, 2006).

Sustainability and production challenges

Sustainable production of probiotic yeasts involves exploring alternative fermentation processes and utilizing waste streams from the dairy industry. Wild yeasts from natural environments and processed foods can serve as viable sources for probiotics. For instance, Saccharomyces cerevisiae var. boulardii has demonstrated robust survival strategies that enable it to withstand harsh gastrointestinal conditions better than many probiotic bacteria (Gürkan Özlü et al., 2022). Additionally, yeasts such as Debaryomyces, Hanseniaspora, Pichia, Meyerozyma, and Torulaspora exhibit beneficial probiotic characteristics (Tullio, 2022). Ensuring safety and efficacy when sourcing yeasts from food waste, including dairy industry by-products, is crucial. This comprehensive approach is necessary to maintain both effectiveness and safety in probiotic applications (Tullio, 2022).

Technological innovations and safety considerations

Advancements in genetic engineering and biotechnology offer the potential to develop probiotic yeasts with enhanced functionalities and targeted health benefits. These technologies allow for the creation of genetically modified yeasts that can meet evolving consumer demands and drive innovation within the dairy industry (Tullio, 2022). However, challenges such as excessive gas and alcohol production by certain yeasts, like S. boulardii, need to be addressed. Studies indicate that this yeast can ferment sugars to produce alcohol and gas, which may affect the flavor and texture of dairy products (Lourens-Hattingh & Viljoen, 2001). Additionally, while opportunistic yeast species such as Candida albicans and Cryptococcus neoformans are generally not aggressive pathogens, they can cause infections in immunocompromised individuals (Low & Rotstein, 2011). Careful selection of yeast strains, optimization of fermentation conditions, and rigorous safety assessments are crucial to mitigate these risks and maximize the benefits of probiotic yeasts (Dong et al., 2023).

Health benefits of probiotics yeast strains

Enhanced health benefits (Fig. 7)

Fig. 7

Enhanced health benefits of the consumption of products containing probiotic yeasts

Enhanced digestion

Growing interest surrounds the potential benefits of yeasts, such as Saccharomyces boulardii CNCM I-745, which has been extensively studied for its digestive and specific health benefits. Specific strains of probiotic yeasts, such as Saccharomyces boulardii CNCM I-745, contribute to gut health by fostering a balanced microbial community. These yeasts compete with harmful bacteria for resources and adhesion sites, promoting the proliferation of beneficial bacteria and supporting overall gut function. For example, Saccharomyces boulardii CNCM I-745 has been shown to prevent and treat antibiotic-associated diarrhea and Clostridium difficile infections, highlighting its specific probiotic effects (McFarland, 2010).

In evaluating these yeasts for probiotic use, it is essential that the chosen yeast strain exhibits key probiotic attributes, such as the ability to adhere to the intestinal epithelium, withstand gastric acidity, and survive exposure to bile salts (Gao et al., 2021). These characteristics are critical for the yeast to effectively colonize the gut and confer health benefits. Additionally, the strain must be nonpathogenic and nontoxic to ensure the safety of the probiotic product (Sanders et al., 2010).

A crucial aspect of overall health is a healthy gut, and probiotic yeasts play a role in stimulating the production of immunoglobulins and enhancing immune cell activity, thereby supporting immune health. The anti-inflammatory properties of certain probiotic yeasts can modulate the inflammatory response in the gut, potentially leading to improved digestion and reduced gastrointestinal discomfort. Moreover, these yeasts may enhance nutrient absorption by promoting a healthy gut lining and aiding in the breakdown of specific substances. Notably, Saccharomyces boulardii has been a focal point of research due to its effectiveness in preventing and alleviating diarrhea associated with diverse causes, such as antibiotic use, infections, and inflammatory bowel diseases. Further studies are necessary to comprehensively understand the mechanisms of action and efficacy of probiotic yeasts under various conditions. Consulting with a healthcare professional is advisable before integrating probiotic yeasts into one's routine, especially for individuals with preexisting health conditions or those taking medications. Additionally, the benefits of probiotics can vary based on the stain, dose, and individual health factors (Kabiri & Vogl, 2023; Lara-Hidalgo et al., 2017; Staniszewski & Kordowska-Wiater, 2021).

Nutrient enrichment

Nutrient enrichment of probiotic yeast involves enhancing its nutritional content to provide additional health benefits. By adjusting growth conditions such as temperature, pH, and oxygen levels, or by genetically engineering the yeast, it's possible to improve nutrient synthesis and metabolic pathways, thereby enhancing the yeast's overall nutritional profile. This enrichment not only contributes to better health outcomes but also improves the resilience and functionality of the yeast in the gastrointestinal environment, particularly in acidic and bile-rich conditions (Shruthi et al., 2022).

Alleviation of lactose intolerance

The potential of the yeast Saccharomyces boulardii to mitigate symptoms associated with lactose intolerance has been examined. Although traditionally linked with probiotic bacteria, research indicates that specific yeasts may play a role in enhancing lactose digestion. The principal cause of lactose intolerance is lactase deficiency, the enzyme responsible for lactose breakdown. Certain probiotic yeasts stains, via fermentation, have been found to produce lactase or other enzymes that facilitate lactose digestion. Through the fermentation process, these yeasts can transform lactose into simpler sugars such as glucose and galactose. This digestion mechanism may render lactose more easily absorbable for individuals with lactose intolerance (Ibrahim et al., 2021).

Prevention of diarrheal diseases

The role of probiotics in preventing and managing diarrheal diseases has been well established. Specific strains, including Lactobacillus GG, and some species like Lactobacillus reuteri, Saccharomyces boulardii, and Bifidobacterium, have shown significant benefits in the treatment of diarrhea (Guandalini, 2011). These agents have proven effective against conditions such as diarrhea and diarrhea in young children caused by rotaviruses (Huang et al., 2021).

Enhanced immune stimulation

Potential probiotic yeasts, such as Saccharomyces boulardii, have been investigated for their ability to enhance immune stimulation. While probiotics are often associated with bacteria, certain yeasts have demonstrated immune-modulating effects. Probiotic yeasts may stimulate the production of immunoglobulins, which are antibodies that play a crucial role in the immune response. This can enhance the body's ability to recognize and fight pathogens. As probiotic yeasts reside in the gastrointestinal tract, they can interact with the gut-associated lymphoid tissue (GALT). This interaction may lead to the stimulation of mucosal immune responses, contributing to local and systemic immune enhancement (Angulo et al., 2023).

In addition, studies have shown that lipopolysaccharides (LPS), which are major components of the outer membrane of Gram-negative bacteria, have significant negative effects on the nervous system. LPS activates TLR-4 receptors in astrocytes and neurons, triggering neuroinflammatory processes that are associated with neurodegenerative diseases like Alzheimer’s (Gorina et al., 2011). Increased plasma LPS levels can alter neuronal cholesterol metabolism, promoting the aggregation and fibril formation of amyloid-beta (Aβ), which leads to accelerated neuronal death (Martins, 2015). Additionally, LPS is associated with Aβ metabolism in the brain through the CD14 receptor and may cause neuronal death by interfering with the nuclear receptor Sirtuin 1 (Sirt 1), which plays a crucial role in regulating transcription factors and cellular proteins related to neuronal survival (Jellinger, 2012).

Therefore, it can be concluded that probiotics can positively affect the gut microbiota and reduce the level of plasma LPS. Probiotic yeasts such as Saccharomyces boulardii strain help maintain a balanced intestinal microbiota by promoting the growth of beneficial bacteria such as Lactobacillus spp. and Bifidobacterium spp, thereby preventing the transfer of LPS to the bloodstream (Arroyo-Espliguero et al., 2004). These species can improve the integrity of the intestinal barrier and reduce its permeability, restrict the transfer of LPS to the bloodstream and thereby reduce systemic inflammation. In addition, the composition of probiotics in food can determine the composition of gut bacteria and the fight against dysbiosis (Bermudez-Brito et al., 2012).

Pathogen inhibition

Probiotics play a pivotal role in preventing infection by competing with pathogens for binding sites on epithelial cells. Similarly, certain probiotic yeasts, such as Saccharomyces boulardii, exhibit this competitive exclusion effect. Studies have shown that Saccharomyces boulardii can adhere to intestinal epithelial cells and prevent the attachment and colonization of harmful pathogens, including Clostridium difficile and Escherichia coli (McFarland, 2010). This mechanism helps maintain a balanced gut microbiota and protect against infections. Moreover, they can hinder the growth of pathogenic bacteria through the production of bacteriocins, such as nisin. The generation of lactic acid by probiotics also aids in reducing the pH of intestinal contents, thereby inhibiting the proliferation of invasive pathogens such as Salmonella spp. and specific strains of E. coli (Piatek et al., 2020).

Cancer prevention

Probiotic cultures have been shown to reduce exposure to chemical carcinogens by detoxifying ingested carcinogens. Similarly, certain probiotic yeasts, such as Saccharomyces boulardii, exhibit detoxification properties. Studies have demonstrated that Saccharomyces boulardii can bind to and inactivate various mycotoxins, such as aflatoxins, thereby reducing their bioavailability and potential harmful effects (Peltonen et al., 2000). This detoxification ability contributes to the protective role of probiotic yeasts against chemical carcinogens. They can also bind to mutagenic compounds in the intestine, thereby diminishing their absorption. Furthermore, probiotics can inhibit the growth of bacteria responsible for converting procarcinogens into carcinogens, resulting in a reduction in carcinogen levels in the intestine (Śliżewska et al., 2021). Additionally, stimulating the immune system with probiotic microbes helps to better defend against cancer cell proliferation (Górska et al., 2019).

Blood cholesterol and hyperlipidemia control

Managing blood cholesterol levels is crucial for cardiovascular health, and researchers have explored the potential of Saccharomyces boulardii, to influence lipid profiles. Probiotic yeast such as Saccharomyces boulardii CNCM I-745 has been studied for its ability to interfere with the absorption of dietary cholesterol in the intestines, potentially leading to a decrease in the amount of cholesterol entering the bloodstream. These yeasts can influence the metabolism of bile salts, which are essential for the digestion and absorption of fats, including cholesterol. Through modifications in bile salt composition, probiotic yeasts may play a role in impacting lipid metabolism, contributing to a potential reduction in cholesterol absorption (Ryan et al., 2015).

Inflammatory bowel disease (IBD)

Probiotics have demonstrated potential benefits in treating inflammatory bowel diseases (IBDs) such as ulcerative colitis, pouchitis, and Crohn's disease. By improving intestinal mobility and possibly reducing gut pH, lactic acid bacteria may relieve symptoms (Sanders & Klaenhammer, 2001). Additionally, probiotic combination therapies have been reported to benefit patients with IBD (Schultz & Sartor, 2000). For instance, Saccharomyces boulardii has been found to prolong remission and reduce relapse rates in patients with Crohn's disease, while both Saccharomyces boulardii CNCM I-745 and Lactobacillus rhamnosus GG have been reported to increase secretory IgA levels in the gut (Isaacs & Herfarth, 2008).

Irritable bowel syndrome (IBS)

Irritable bowel syndrome (IBS) is a prevalent gastrointestinal disorder marked by symptoms such as abdominal pain, bloating, gas, and changes in bowel habits. Saccharomyces boulardii, has been studied for its potential to alleviate symptoms related to IBS. By impacting the composition and equilibrium of the gut microbiota, probiotic yeast may aid in rectifying microbiota imbalances commonly linked to IBS, offering a potential avenue for restoring harmony in the gut (Cayzeele-Decherf et al., 2017).

Novel product development using probiotic yeasts

The multifaceted biological activities of yeasts position them as promising candidates for a broad spectrum of applications beyond the realm of food. While they are renowned for their pivotal role in flavor development during fermentation, their antagonistic actions against detrimental bacteria and fungi are now well-documented (Souza et al., 2021). These beneficial activities stem from various mechanisms, including competition for nutrients, acidification of the growth environment, tolerance to high ethanol concentrations, and secretion of antimicrobial compounds such as antifungal toxins or "myosin" and antibacterial agents. Despite the predominant focus on Lactobacillus spp and Bifidobacterium spp in the design of probiotic-containing foods, Saccharomyces cerevisiae var. boulardii has long been recognized for its efficacy in treating gastroenteritis (Tullio, 2022). The health benefits conferred by probiotic yeasts, coupled with their potential to enhance product characteristics, have led to a growing emphasis among scientists and researchers on developing food products incorporating these microorganisms. As a result, the exploration of probiotic yeasts in the context of food production is expanding rapidly.

Conclusion

Yeast has a long history of use in various food industries, including dairy products. They are single-celled fungi belonging to the phyla Ascomycota and Basidiomycota and have been utilized for approximately 5000 years in the preparation of bread and beverages. Yeasts offer numerous useful properties, with their probiotic effects being one of their unique characteristics. While most research on probiotics has focused on lactic acid bacteria and bifidobacteria, there is growing recognition of the importance of incorporating yeasts as probiotic food supplements. Certain yeast strains, such as Saccharomyces boulardii, have demonstrated therapeutic effects on gastrointestinal conditions and are widely used in commercial probiotic preparations. The selection of probiotic yeasts is based on their ability to survive in the gastrointestinal environment, interact effectively with host systems, demonstrate safety, and exhibit antipathogenic activity. Probiotic yeasts have been found in various dairy products, including yogurt, kefir, kumis, and cheese. These compounds contribute to the fermentation process, flavor development, and overall quality of these products. The compatibility of probiotic yeasts with different dairy matrices and the impact of processing conditions on their viability and functionality are important factors to consider in the development of probiotic dairy products. Micro-encapsulation techniques can be employed to improve yeast viability during processing and storage. Additionally, strain-specific variations in yeast properties should be carefully evaluated to optimize the probiotic potential of these strains in dairy products. Overall, probiotic yeasts represent a promising area of research and development in the food industry, with the potential to provide various health benefits to consumers when incorporated into dairy products and other functional foods. Continued exploration and understanding of their properties and interactions with the host system will further enhance their application and impact on human health.